US4924082A - Optical scanning device, mirror objective suitable for use in said device and optical write and/or read apparatus provided with said device - Google Patents

Optical scanning device, mirror objective suitable for use in said device and optical write and/or read apparatus provided with said device Download PDF

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US4924082A
US4924082A US07/319,773 US31977389A US4924082A US 4924082 A US4924082 A US 4924082A US 31977389 A US31977389 A US 31977389A US 4924082 A US4924082 A US 4924082A
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radiation
sub
grating
scanning device
gratings
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Willem G. Opheij
Josephus J. M. Braat
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US Philips Corp
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US Philips Corp
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1381—Non-lens elements for altering the properties of the beam, e.g. knife edges, slits, filters or stops
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
    • G10L19/08—Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
    • G10L19/12—Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/1055—Disposition or mounting of transducers relative to record carriers
    • G11B11/10556—Disposition or mounting of transducers relative to record carriers with provision for moving or switching or masking the transducers in or out of their operative position
    • G11B11/10558—Disposition or mounting of transducers relative to record carriers with provision for moving or switching or masking the transducers in or out of their operative position in view of the loading or unloading of the carrier
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
    • G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
    • G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
    • G11B11/10595—Control of operating function
    • G11B11/10597—Adaptations for transducing various formats on the same or different carriers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B17/00—Guiding record carriers not specifically of filamentary or web form, or of supports therefor
    • G11B17/02—Details
    • G11B17/04—Feeding or guiding single record carrier to or from transducer unit
    • G11B17/041—Feeding or guiding single record carrier to or from transducer unit specially adapted for discs contained within cartridges
    • G11B17/043—Direct insertion, i.e. without external loading means
    • G11B17/0434—Direct insertion, i.e. without external loading means with mechanism for subsequent vertical movement of the disc
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
    • G11B19/02—Control of operating function, e.g. switching from recording to reproducing
    • G11B19/12—Control of operating function, e.g. switching from recording to reproducing by sensing distinguishing features of or on records, e.g. diameter end mark
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B23/00—Record carriers not specific to the method of recording or reproducing; Accessories, e.g. containers, specially adapted for co-operation with the recording or reproducing apparatus ; Intermediate mediums; Apparatus or processes specially adapted for their manufacture
    • G11B23/02—Containers; Storing means both adapted to cooperate with the recording or reproducing means
    • G11B23/03—Containers for flat record carriers
    • G11B23/0301—Details
    • G11B23/0302—Auxiliary features
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B25/00—Apparatus characterised by the shape of record carrier employed but not specific to the method of recording or reproducing, e.g. dictating apparatus; Combinations of such apparatus
    • G11B25/04—Apparatus characterised by the shape of record carrier employed but not specific to the method of recording or reproducing, e.g. dictating apparatus; Combinations of such apparatus using flat record carriers, e.g. disc, card
    • G11B25/043—Apparatus characterised by the shape of record carrier employed but not specific to the method of recording or reproducing, e.g. dictating apparatus; Combinations of such apparatus using flat record carriers, e.g. disc, card using rotating discs
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B33/00—Constructional parts, details or accessories not provided for in the other groups of this subclass
    • G11B33/12—Disposition of constructional parts in the apparatus, e.g. of power supply, of modules
    • G11B33/121—Disposition of constructional parts in the apparatus, e.g. of power supply, of modules the apparatus comprising a single recording/reproducing device
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/002—Recording, reproducing or erasing systems characterised by the shape or form of the carrier
    • G11B7/0037—Recording, reproducing or erasing systems characterised by the shape or form of the carrier with discs
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
    • G11B7/0909—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only by astigmatic methods
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
    • G11B7/0916—Foucault or knife-edge methods
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1353—Diffractive elements, e.g. holograms or gratings
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B7/1374—Objective lenses
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L2019/0001—Codebooks
    • G10L2019/0011—Long term prediction filters, i.e. pitch estimation
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L2019/0001—Codebooks
    • G10L2019/0012—Smoothing of parameters of the decoder interpolation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B2007/13725—Catadioptric lenses, i.e. having at least one internal reflective surface

Definitions

  • the invention relates to a scanning device for optically scanning an information plane, which device comprises a radiation source supplying a scanning beam and a mirror objective for focusing the scanning beam to a scanning spot in the information plane.
  • the invention also relates to a mirror objective suitable for use in this scanning device and to a write an/or read apparatus provided with such a device.
  • Scanning an information plane is to be understood to mean both scanning for reading a prerecorded information plane and scanning for writing information in this plane by means of a radiation beam which is intensity-modulated in accordance with the information to be recorded. If a magneto-optical record carrier is recorded, the radiation beam may also have a constant intensity and the magnetic field may be modulated in accordance with this information to be recorded.
  • the information plane may be a plane of an optical record carrier, but also a surface or a plane in an object to be examined, the scanning device then forming part of, for example a microscope.
  • a scanning device as described in the opening paragraph, intended for reading an optical record carrier is known from British Patent Specification No. 1,541,596.
  • This specification describes an optical scanning device which includes an objective comprising two mirrors whose reflective sides face each other. The one mirror is concave and its reflective side faces the record carrier. The other mirror, which is much smaller, is convex and its reflective side faces the radiation source. The radiation from the radiation source reaches the convex mirror via a passage in the larger concave mirror. The radiation is subsequently reflected towards the concave mirror and focused by this mirror to a radiation spot in the information plane of the record carrier.
  • the known objective forms part of a two-stage focusing system in which the entire mirror system is suspended in a magnetic coil by which the position of the objective with respect to the record carrier is controlled.
  • the small mirror is mounted on a piece of piezo-electric material and can be moved up and down with the aid thereof so that a small extent of defocus is periodically produced in the information plane, which defocus is detected by a detection device and from which subsequently a focus-error signal is derived which is used for re-adjusting the position of the objective by means of the magnetic coil.
  • the known scanning device has a rather complicated structure and is sensitive to mechanical perturbations.
  • the scanning device is characterized in that the mirror objective comprises a transparent body having a first surface facing the radiation source and a second surface remote from the radiation source, said first surface having a first radiation window which is located symmetrically around the optical axis of the mirror objective and having a first reflector surrounding said window, said second surface having a second reflector which is located symmetrically around the optical axis and a second radiation window surrounding the second reflector, the radiation path through the mirror objective extending via passage through the first window, reflection from the second reflector, reflection from the first reflector and passage through the second window, at least one of the two windows having an aspherical surface.
  • An aspherical surface in a lens system is understood to mean a lens element surface whose fundamental shape is spherical but whose real shape deviates therefrom to a small extent in order to correct for spherical aberration which would be produced when the lens element has spherical surfaces.
  • the spherical fundamental shape may also have an infinitely large radius of curvature so that the said aspherical surface has a flat fundamental shape.
  • the scanning device comprising the said mirror objective is not only compact because the radiation path in this objective is folded, but the mirror objective is also well corrected for spherical aberration. According to the invention this is achieved by giving a radiation window an aspherical shape. Its advantage is that the required accuracy of the shape of the aspherical surface may be considerably smaller, for example by a factor of 5 to 6, than the required accuracy of the shape of a reflective aspherical surface. This provides the possibility of manufacturing the mirror objective and hence the complete scanning device at reasonably low cost.
  • the preferred embodiment of the scanning device according to the invention is characterized in that the second radiation window has an aspherical surface.
  • This embodiment is preferred to the first embodiment in which the first radiation window has an aspherical surface, because a larger diffraction-limited image field can be obtained, than with the first embodiment.
  • the scanning device can be used for scanning a radiation-transparent information plane.
  • the inventive concept is, however, used to best advantage in a scanning device for scanning a radiation-reflecting information plane in which radiation from the information plane is returned and traverses the mirror objective so as to be focused on a radiation-sensitive detection system which is arranged on the same side of the mirror objective as the radiation source.
  • a scanning device is further characterized in that the mirror objective comprises a beam-separating element for spatially separating the beam emitted by the radiation source and the beam reflected from the information plane and focused by the mirror objective.
  • the beam-separating element may be a semi-transparent mirror or cube arranged on the first radiation window.
  • the scanning device comprising a beam-separating element is preferably further characterized in that the beam-separating element is a diffraction element.
  • This diffraction element can be relatively simply arranged on one of the surfaces of the mirror objective and moreover it can fulfil a second function to be described hereinafter.
  • a preferred embodiment of the scanning device comprising a mirror objective provided with a diffraction element is characterized in that the diffraction element is reflective and is arranged on the second reflector.
  • a second embodiment of such a scanning device is characterized in that the diffraction element is radiation-transparent and is arranged on the first radiation window.
  • the diffraction element may alternatively be accommodated in the body of the mirror objective.
  • This body may comprise two parts, the diffraction element being arranged on one of the two facing surfaces of the two parts.
  • the diffraction element may be formed in such a manner that it renders the beam incident on the detection system suitable for focus-error detection, in conjunction with an adapted detection system.
  • a focusing error is understood to mean a deviation between the focusing plane of the mirror objective and the information plane.
  • a first embodiment of the scanning device comprising a diffraction element shich is adapted for focus-error detection is characterized in that the diffraction element is an element introducing astigmatism and in that the radiation-sensitive detection system comprises four detectors which are arranged in four different quadrants around the chief ray of the beam diffracted by the diffraction element.
  • the element introducing astigmatism may be a linear grating which, due to its location in a non-parallel beam, introduces a certain extent of astigmatism in this beam.
  • the shape of the radiation spot formed by this beam on the detection system is determined by the degree of focusing on the information plane.
  • this radiation spot is deformed to an elliptical spot whose major axis, dependent on the defocusing sign is located in one the two mutually perpendicular directions, also referred to as the astigmatic directions.
  • the separating strip between the four detectors extend at angles of approximately 45° to the astigmatic directions.
  • the diffraction element may be a diffraction grating having straight grating strips and a linear grating period.
  • the astigmatic diffraction element is a holographic grating having curved grating strips and a non-linear grating period. Imaging errors such as coma can be corrected by adapting the curvatures.
  • a second focus-error detection possibility which is preferred to the above-mentioned, so-called astigmatic method as far as temperature sensitivity and ease of control is concerned, is realised in an embodiment which is characterized in that the first diffraction element is a diffraction grating comprising two sub-gratings and splitting the diffracted scanning beam into two sub-beams and in that the composite detection system comprises two detector pairs, the first and second sub-beams co-operating with a first and a second detector pair, respectively.
  • the scanning spot is re-imaged in two radiation spots on the detector pairs.
  • Each radiation spot shifts transversely of the separating strip of the associated detector pair in dependence upon a focusing error of the scanning beam relative to the information plane. This shift can be detected by comparing the output signals of the detectors.
  • This focus-error detection method is known as the double Foucault method.
  • a preferred embodiment of the last-mentioned device is characterized in that the sub-gratings have a varying grating period and in that the grating strips of the sub-gratings are curved.
  • the composite grating Due to the varying grating period and the curved grating strips the composite grating has a lens action and by displacing this grating in the direction of the bounding line of the sub-gratings the energy distribution of the radiation spots can be rendered symmetrical with respect to the associated detector pairs, inter alia because the imaging distance of the assembly of objective system and the grating is adapted to the distance, in the direction of the optical axis, between the diode laser and the detectors. This is particularly important if the detectors, in the form of photodiodes, and the diode laser are combined in one component and are fixed relative to each other.
  • a composite grating having varying grating periods and curved grating strips, which grating is also referred to as hologram, provides the possibility of correcting imaging errors such as coma and astigmatism which may occur when using a grating with straight grating strips.
  • the first embodiment is characterized in that the grating strips of the one sub-grating have the same main direction as those of the other sub-grating, in that the average grating periods of the sub-gratings are different and in that the detector pairs are juxtaposed in a direction parallel to the bounding line between the sub-gratings.
  • the sub-beams of the scanning beam are diffracted in the same direction but at different angles.
  • the second embodiment is characterized in that the sub-gratings have the same average grating period, while the main directions of the grating strips of the one sub-grating extend at a first angle and those of the other sub-grating extend at a second angle to the bounding line of the two sub-gratings and in that the detector pairs are juxtaposed in a direction transversely of the direction of the said bounding line.
  • the sub-beams of the scanning beam are preferably diffracted at the same angles but in different directions. This embodiment is preferred to the previous embodiment due to its better assembly tolerances, adjusting facilities and stability.
  • the use of a mirror objective with a transparent body in a scanning device may have further advantages with regard to the positioning of the radiation source and the radiation-sensitive detection system.
  • an embodiment of the scanning device is characterized in that the radiation source is connected to the first radiation window.
  • the radiation source is, for example a semiconductor laser a radiation-emitting surface of which is provided on the radiation window, or the radiation source is connected to the radiation window via an optical fibre or a series of fibres.
  • an embodiment of the scanning device according to the invention provided with a radiation-sensitive detection system may be characterized in that the radiation-sensitive detection system is arranged on the first radiation window in the radiation path of radiation which has been reflected from the information plane and which has traversed the mirror objective.
  • the radiation source, the optical fibres or the radiation-sensitive detection system are secured to the first radiation window by means of, for example a transparent adhesive. This results in a single compact and robust, integrated component accomodating the entire optical section of the scanning device.
  • the various embodiments of the scanning device according to the invention may comprise different types of radiation sources such as, for example, a single semiconductor laser, a semiconductor laser array or another radiation source which can be connected to the mirror objective directly or by means of optical fibres.
  • a single semiconductor laser such as, for example, a single semiconductor laser, a semiconductor laser array or another radiation source which can be connected to the mirror objective directly or by means of optical fibres.
  • FIGS. 1, 2, 3 and 4 show various embodiments of the scanning device
  • FIGS. 5 and 6 show two embodiments of a diffraction element to be used in this device, with which element two sub-beams are obtained,
  • FIGS. 7 and 9 show two embodiments of a diffraction element with which an astigmatic beam is obtained
  • FIGS. 8 and 10 show the radiation-sensitive detection systems asssociated with these diffraction elements
  • FIG. 11 shows a scanning device for a magneto-optical record carrier.
  • FIG. 1 is a sectional view of a portion of an optical record carrier 10 having a reflecting information plane 11.
  • a scanning device comprising a mirror objective 30 and a radiation source 40 is provided close to the record carrier.
  • the radiation source 40 emits a scanning beam 20 which is focused to a scanning spot 21 in the information plane 11 by the mirror objective 30.
  • the entire information plane can be covered by the scanning spot because the scanning device and the record carrier are movable with respect to each other, for example because the record carrier can rotate around an axis (not shown) perpendicular to the plane of the record carrier and because the scanning device can move in the radial direction with respect to the same axis.
  • the scanning beam 20 traverses the mirror objective and the beam enters the transparent body of the objective via the first radiation window 31. Subsequently the scanning beam is reflected on the convex reflector 32, so that the scanning beam widens and is incident on substantially the entire surface of the concave reflector 33.
  • This reflector reflects the scanning beam as a convergent beam which is focused to a scanning spot 21 in the information plane 11 via the radiation window 34 and a portion of the transparent record carrier 10.
  • the beam reflected at the spot 21 is received by the mirror objective again and traverses the reverse path therein to the radiation window 31.
  • the reflected beam may enter the radiation source and when using a semiconductor laser as a radiation source, it can be detected thereby.
  • This so-called feedback read-out is described, for example in German Patent Specification No. 1,584,664.
  • a beam-splitting element Preferably, however, a beam-splitting element.
  • a splitting cube 50 through which a portion of the reflected radiation is separated from the scanning beam 20 and is projected on a radiation-sensitive detection system 60, is arranged in the common radiation path of the emitted and the reflected radiation beams. Since the radiation reflected from the information plane 11 is modulated with the information stored in said information plane and scanned by the radiation spot, the reflected radiation is converted by the system 60 into an electric signal suitable for further processing.
  • the beam focused by the mirror objective 30 exhibits spherical aberration.
  • spherical aberration As is known, inter alia from U.S. Pat. No. 4,668,056, it is possible to correct for this aberration by using aspherical surfaces.
  • the reflecting surface 33 is given an aspherical shape so as to obtain a relatively large diffraction-limited image field.
  • the surface of one or of both radiation windows 31 and 34 is aspherical. Though the image field is then reduced, it has been found that it is still sufficiently large for the envisaged object: scanning a surface by means of a diffraction-limited spot.
  • n 1 is the refractive index of the lens material and n 2 is the refractive index of the surrounding medium.
  • the technique described in U.S. Pat. No. 4,668,056 for giving the surface of a conventional lens an aspherical shape can be used.
  • a mirror objective is then obtained in which the aspherical surface of a radiation window is constituted by the aspherical outer surface of a transparent synthetic material layer which is provided on the spherical surface of this window.
  • the synthetic material may be a polymerisable synthetic matrial, for example a material being cured under the influence of ultraviolet radiation which is applied on the window in a liquid state and is given the desired shape by means of a mould.
  • FIG. 1 shows a preferred embodiment in which the second radiation window 34 is aspherical.
  • the embodiment in FIG. 2 has the advantage of a larger diffraction-limited image field.
  • the embodiment of FIG. 2 is suitable for reading a radiation-reflective information plane 11. The radiation reflected from this plane and received by the mirror objective 30 and condensed in a radiation beam 20' is separated from the beam 20 emitted by the radiation source 40 by means of a diffraction element 39 which is arranged on the radiation window 31.
  • the diffraction element 39 is, for example a diffraction grating having straight grating strips. This grating splits a beam incident thereon into a non-diffracted zero-order sub-beam and into two diffracted first-order sub-beams and a plurality of diffracted higher-order sub-beams.
  • the grating parameters such as the ratio between the width of the strips and those of the intermediate grating strips and, in the case of a phase grating, the shape and the depth of the grating grooves, can be chosen so that the intensity product of the zero-order sub-beam formed at the first passage through the grating and a first-order sub-beam formed at the second passage through the grating is a maximum. It can be ensured that the first-order sub-beams formed at the first passage through the grating 39 are diffracted through such an angle that the radiation of these beams does not reach the detection system 60 after reflection by the information plane 11.
  • the radiation source 40 and the radiation-sensitive detection system 60 are arranged at some distance from the radiation window 31. This provides the advantage that when using a holographic grating as a diffraction element a fine control is possible by moving the mirror objective with this grating relative to the detection system.
  • the radiation source 40 and the detection system 60 are arranged on the radiation window 31.
  • the elements 40 and 60 may alternatively be connected to the window 31 via optical fibres.
  • the grating 39 is now a reflecting grating and is arranged on the second reflector 32.
  • FIG. 4 shows an embodiment of the scanning device in which the diffraction grating 39 is arranged within the body of the mirror objective 30.
  • This body is divided into two parts 36 and 37 in principle consisting of the same material and the grating is provided on one of the facing surfaces of the parts 36 and 37.
  • the grating 39 may be formed in such a way that the beam originating from this grating and facing the detection system 60 is suitable for supplying, in conjunction with an adapted detection system a focus error signal.
  • a first embodiment of such a grating with the associated detection system is shown diagrammatically in FIG. 5.
  • the beam 20' is shown by way of its cross-section at the area of the grating 39.
  • This grating 39 comprises two sub-gratings 41 and 42 which are separated from each other by the line 43.
  • the grating strips of the sub-gratings are denoted by the reference numerals 44 and 45, respectively. These grating strips are separated by intermediate strips 46 and 47.
  • the sub-gratings have the same grating period, but the main directions of the preferably curved grating strips 44 of the sub-grating 41 extend at a first angle to the bounding line 43, while the main directions of the curved grating strips 45 of the second sub-grating 42 extend at a second, preferably equally large but opposite angle to the bounding line.
  • the sub-beams are diffracted in a direction substantially transversely of the main directions. Since the main directions are different, the sub-beams 20 a ' and 20 b ' are diffracted at different angles in YZ plane.
  • the references X, Y and X are the axes of a system of coordinates whose origin 0 coincides with the centre of the radiation-emitting surface of the diode laser 40.
  • Radiation-sensitive detectors in the form of photodiodes 48, 49 and 50, 51, which are separated by narrow strips 52 and 53, are associated with each of the sub-beams 20 a ' and 20 b ', respectively. These detectors are positioned in such a way that in the case of a correct focusing of the beam 20 on the information plane 11 the intensity distribution of the radiation spots 22 a and 22 b formed by the sub-beams 20 a ' and 20 b ' is symmetrical relative to the detectors 48, 49 and 50, 51, respectively. When a focusing error occurs, the radiation spots 22 a ' and 22 b ' will become asymmetrically larger and the centre of the radiation distribution of each radiation spot is displaced transversely of the separating strips 52 and 53, respectively, of the associated detector pair.
  • the focus-error signal S f will be given by:
  • a signal which is proportional to the information being read, or the information signal S i is given by
  • the scanning beam 20 and the reflected beam 20' are shown by means of their cross-section in the plane of the grating, with the sub-beams 20 a ' and 20 b '.
  • the main directions of the preferably curved grating strips of the two sub-gratings 42 and 43 now extend at the same angle to the bounding line 43, while the average grating periods of the two sub-gratings are different. Consequently, the angle at which the sub-beam 20 a ' is diffracted is different from the angle at which the sub-beam 20 b ' is difracted. This means that in the plane of the detectors 48, 49, 50 and 51 the radiation spots 22a and 22b are displaced relative to each other in the direction of the bounding line 43.
  • the sub-gratings 41 and 42 may have straight grating strips and a constant grating period. However, preferably a type of grating, also referred to as holograms, is used which has a varying grating period, the variation in the period being, for example of the order of several percents of the average grating period. Moreover, the grating strips of the two sub-gratings are curved, as is shown in FIGS. 5 and 6. Thus, these sub-gratings have a variable lens action. Due to the varying grating period the positions of the radiation spots 22 a and 22 b can be varied by displacing the grating 9 in its own plane.
  • Aberrations in a direction perpendicular to the direction of the bounding line 43 can be minimised by suitable curvatures of the grating strips.
  • the possibility of moving the positions of the radiation spots is particularly important if an integrated laser-photodiode unit is used, i.e. a component in which the diode laser and the photodetectors are arranged on one support and are therefore fixed relative to each other and thus have a fixed mutual distance in the Z direction. This distance is subject to close manufacturing tolerances, and cannot be corrected during assembly of the device by displacing the photodiodes relative to the laser diode in the Z direction.
  • diffraction grating having curved grating strips, or hologram as compared with a grating having straight grating strips is that the optical aberrations such as coma and astigmatism, which may occur when using the last-mentioned grating, can be avoided in the first-mentioned grating by taking these aberrations into account when manufacturing this holographic grating and by adapting the curvatures of the grating strips accordingly.
  • FIG. 7 shows an embodiment of a grating 70 converting the reflected scanning beam 20' into an astigmatic beam 20 1 '.
  • This grating has straight grating strips 71 and a linearly varying grating period.
  • the grating is dimensioned in such a way that the radiation of the beam 20' is largely diffracted in one order, for example the first order.
  • the first-order beam 20 1 ' is no longer focused in one point but in two mutually perpendicular focal lines 75 and 76, the line 75 being located in a position where the beam 20 1 ' would be focused if the grating were not astigmatic.
  • the focal lines 75 and 76 are simultaneously displaced in the same direction and over the same distance.
  • a so-called four-quadrant detector 80 is arranged in a plane approximately halfway between the positions occupied by the astigmatic focal lines, if the scanning beam is sharply focused on the information plane.
  • This detector shown in FIG. 8, comprises four detectors 81, 82, 83 and 84 which are arranged in four different quadrants around the chief ray of the diffracted beam 20 1 '. If the scanning beam is sharply focused on the information plane 11, the radiation spot 22' formed by the beam 20 1 ' in the plane of the detectors is round, as is illustrated by the solid line circle in FIG. 8. If a focusing error occurs, the radiation spot 22 1 ' is deformed to an elliptical spot, as illustrated by the broken line ellipses in FIG. 8.
  • the major axis of the ellipse extends at an angle of 45° to the separating strips 85 and 86, the sign of the angle being determined by the sign of the focusing error. If the signals of the detectors 81, 82, 83 and 84 are represented by S 81 , S 82 , S 83 and S 84 , the focus-error signal S f will be given by:
  • the grating 70 may be in the form of a holographic grating having curved grating strips, thus providing the said adjusting and correction possibilities.
  • FIG. 9 shows an embodiment of the scanning device specially suitable for writing and reading so-called magneto-optical record carriers.
  • record carriers and write and read apparatuses therefor are described in the inter alia the Article "Erasable magneto-optical recording” in "Philips Technical Review” Vol. 42, No. 2, 1985, pages 37-47.
  • a so-called differential method is used when reading a magneto-optical record carrier.
  • the radiation which is reflected by the information plane and whose direction of polarisation is time-modulated in accordance with the information which has been read, is split after passage through the objective into two mutually perpendicularly polarised sub-beams which are incident on separate detectors.
  • beam splitting is realised by means of a polarisation-sensitive beam splitter.
  • Polarisers 90 and 91 are arranged between the detectors 60 1 and 60 2 so that the beam 20 1 ' incident on the detector 61 1 has a first direction of polarisation and the beam 20 2 ' incident on the detector 60 2 has a second direction of polarisation which is perpendicular to the first direction of polarisation.
  • the grating 39 is provided on the first radiation window 31.
  • this grating is preferably provided on the reflector 32 because then the scanning device can be constructed in the most compact manner. This also applies to the other embodiments.
  • the invention has been described for use in a read apparatus, but it may alternatively be used in a write apparatus or in a combined write-read apparatus in which during recording the focusing and the tracking of the write beam are monitored.
  • the focus-error and tracking-error detection systems described do not utilise special properties of the information surface 2. It is merely necessary and adequate that this surface is reflecting. Therefore the invention may be used in various scanning devices.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Audiology, Speech & Language Pathology (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • Computational Linguistics (AREA)
  • Human Computer Interaction (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Optical Recording Or Reproduction (AREA)
  • Lenses (AREA)
  • Optical Head (AREA)
  • Diffracting Gratings Or Hologram Optical Elements (AREA)
  • Instruments For Viewing The Inside Of Hollow Bodies (AREA)
US07/319,773 1988-12-13 1989-03-07 Optical scanning device, mirror objective suitable for use in said device and optical write and/or read apparatus provided with said device Expired - Fee Related US4924082A (en)

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NL8803048 1988-12-13
NL8803048A NL8803048A (nl) 1988-12-13 1988-12-13 Optische aftastinrichting, spiegelobjektief geschikt voor toepassing daarin en optische inschrijf- en/of uitleesapparaat voorzien van de aftastinrichting.

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US5029255A (en) * 1988-12-13 1991-07-02 U.S. Philips Corporation Optical scanning device including mirror objective having two windows at least one having an aspherical surface
US5161045A (en) * 1990-06-28 1992-11-03 The United States Of America As Represented By The Secretary Of The Air Force Large field of view light beam transceiver having small motion of optics
US5408547A (en) * 1993-02-19 1995-04-18 Motorola, Inc. Optical read/write head
US5883745A (en) * 1997-06-30 1999-03-16 Polycom, Inc. Mirror assembly and method
US6664998B1 (en) * 1999-10-01 2003-12-16 Alps Electric Co., Ltd. Compound optical device, compound optical unit including the compound optical device, and optical pickup apparatus including the compound optical unit
WO2017198489A1 (en) * 2016-05-19 2017-11-23 Koninklijke Philips N.V. Compact laser sensor
US11221565B2 (en) * 2018-04-11 2022-01-11 Asml Netherlands B.V. Level sensor and lithographic apparatus

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US5465247A (en) * 1992-05-14 1995-11-07 Olympus Optical Co., Ltd. Optical head
EP0627735B1 (de) * 1993-06-03 1999-10-06 THOMSON multimedia Optisches System zur Wiedergabe und/oder Aufzeichnung von Information
WO1996030903A2 (en) * 1995-03-29 1996-10-03 Philips Electronics N.V. Optical unit comprising a radiation source, a detector and a grating, and scanning device including the optical unit
DE19740243C1 (de) * 1997-09-12 1999-02-11 Stn Atlas Elektronik Gmbh Optischer Sender zum Aussenden von Lichtsignalen
EP0954859B1 (de) * 1997-11-22 2006-10-18 Samsung Electronics Co., Ltd. Katadioptrisches optisches system, optischer kopf, optisches plattenlaufwerk mit dem system sowie optische platte
US6212153B1 (en) * 1998-07-06 2001-04-03 Read-Rite Corporation High NA solid catadioptric focusing device having a flat kinoform phase profile
KR100530170B1 (ko) * 1999-03-30 2005-11-22 삼성전자주식회사 니어필드를 이용한 광픽업시스템
KR100554071B1 (ko) * 1999-04-21 2006-02-22 삼성전자주식회사 니어필드를 발생하는 집속광학계
KR100644566B1 (ko) 1999-09-29 2006-11-13 삼성전자주식회사 고밀도 광집속을 위한 대물렌즈 및 이를 채용한 광픽업장치
KR100657247B1 (ko) * 1999-11-30 2006-12-19 삼성전자주식회사 고밀도 광집속을 위한 대물렌즈 및 이를 채용한광픽업장치
KR100439373B1 (ko) * 2001-09-13 2004-07-09 엘지전자 주식회사 이종 기록매체 호환 광픽업 장치
JP2006155843A (ja) * 2004-12-01 2006-06-15 Matsushita Electric Ind Co Ltd 光ヘッド
US7619820B2 (en) 2005-02-09 2009-11-17 I Win Technology Co., Ltd. Dot matrix holograms with spatially varying period
CN114216657A (zh) * 2021-12-14 2022-03-22 合肥工业大学 一种凹非球面镜的改进补偿检测系统及其检测方法

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US5029255A (en) * 1988-12-13 1991-07-02 U.S. Philips Corporation Optical scanning device including mirror objective having two windows at least one having an aspherical surface
US5161045A (en) * 1990-06-28 1992-11-03 The United States Of America As Represented By The Secretary Of The Air Force Large field of view light beam transceiver having small motion of optics
US5408547A (en) * 1993-02-19 1995-04-18 Motorola, Inc. Optical read/write head
US5883745A (en) * 1997-06-30 1999-03-16 Polycom, Inc. Mirror assembly and method
US6664998B1 (en) * 1999-10-01 2003-12-16 Alps Electric Co., Ltd. Compound optical device, compound optical unit including the compound optical device, and optical pickup apparatus including the compound optical unit
WO2017198489A1 (en) * 2016-05-19 2017-11-23 Koninklijke Philips N.V. Compact laser sensor
US11221565B2 (en) * 2018-04-11 2022-01-11 Asml Netherlands B.V. Level sensor and lithographic apparatus

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ATE129090T1 (de) 1995-10-15
CA2004994A1 (en) 1990-06-13
DE68924524T2 (de) 1996-05-15
EP0373700B1 (de) 1995-10-11
EP0373700A1 (de) 1990-06-20
CN1026276C (zh) 1994-10-19
NL8803048A (nl) 1990-07-02
CN1043814A (zh) 1990-07-11
DE68924524D1 (de) 1995-11-16
HK169396A (en) 1996-09-20
JPH02214033A (ja) 1990-08-27
ES2080066T3 (es) 1996-02-01
US5029255A (en) 1991-07-02

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